The invention relates to fluid-gauging systems and is particularly concerned with gauging systems for providing an indication of the quantity of fuel in a fuel tank and, more particularly, a fuel tank of an aircraft.
In previous fluid-gauging systems the level of fluid in a reservoir is determined by sensing changes in the value of a capacitor located within the container. The capacitor has two plates, separated by an air-cap which is filled or emptied as the level of fluid changes, thereby altering its capacitance. An alternating electric signal is supplied to the capacitor, and its output, which may be rectified, is supplied to a suitable measuring circuit.
Difficulties have been experienced in the past in providing an accurate indication of fluid quantity because of variations in the alternating signal supplied to the capacitor, temperature changes within the fluid reservoir, and variations in the permittivity of the fluid.